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  1. #1
    Junior Member level 3
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    pls help

    hi everybody,

    i'm havin trouble with this circuit. can somebody explain to me where is the power supply suppose to be for this circuit. there is one port called key +28v and another port which states 28v. which one is the correct positive power supply port. then can i know where is the rf in and rf out signal port is? next, i want to use a osiloscope to measure the rf to be 144mhz. how do i do it? thank you very much. the link for the circuit is below.


    https://www.edaboard.com/viewtopic.php?p=577799#577799

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  2. #2
    Advanced Member level 2
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    pls help

    Read the words in the document.

    The amplifier is keyed by applying 28 V to R1, this turns on the transistor. The collector can be left with 28 V also during receiving.
    The 28V key supply is turned on when the amplifer is being used to transmit. Turning off the bias to the transsitor when receiving will reduce the power consumption and it will generate less noise that might reduce your receiver noise floor slightly.

    [qutoe] want to use a osiloscope to measure the rf to be 144mhz. how do i do it?[/quote]

    You can't check the frequency accurately with an oscilloscope. You can only measure frequency to +/- a few percent. Also most oscilloscopes have 100MHz or less bandwidth. You need a frequency counter to check that you are transmitting on your desired frequency.

    You should also be aware that this amplifier design is not well filtered. Harmonic energy output may be high enough to cause interference to nearby UHF televisions or other radio users.


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